"Entry point could not be located in xul.dll"; Firefox crashes on startup after update, installer also fails.

The full error message is: "The procedure entry point ?WindowsBCryptinitialization@mozilla@@YA_NXZ could not be located in the dynamic link library C:\Program Files\Mozilla Firefox\xul.dll." After accepting that, I get another message that says: "Couldn't load XPCOM." Then, it just quits, with no Crash Reporter dialog. I downloaded a fresh installer, but it takes a couple minutes to even launch, and then just sits there for a long time on the initial screen doing nothing before saying the installation failed. I've restarted my computer twice hoping it was a one-off issue, but there's no change. According to the file information, xul.dll was last changed September 3rd, so it may not be the source of the issue. Perhaps whatever name mangling is responsible for the above entry point changed and now they don't match? I have automatic updates set to "download but don't install", so it downloaded it a few days ago and I just restarted it this evening and the issue occurred. I could understand that maybe something got corrupted during the update, but I have no idea how the installer could ''also'' be failing.